In various types of machinery, it is continuously a problem to seal the opening through which a rotatable shaft protrudes. The problem is manifested in the difficulty of preventing leakage or loss of pressure or loss of vacuum while at the same time avoiding undue shaft friction. The shaft friction can generate heat, cause loss of power, and even damage the machinery. One method of effecting a seal at a joint between a stationary element and a rotatable shaft has been through the use of packing, stuffing, or the like.
In rotary pumps, fans, compressors, agitators, and the like, a shaft projects through a casing in a region known as the "stuffing box" or "packing box." These terms were derived from the fact that in order to separate two environments, for example, to prevent leakage from one environment in a pump into another, and that within the pump and the atmosphere, material had to be stuffed or packed around the shaft where it passed through the casing. However, packing or stuffing causes considerable friction on the shaft.
Another method of effecting a seal has been to utilize O-rings. However, O-rings have presented a problem due to the difficulty of providing a proper material to accommodate the wear thereon when utilized with shafts that operate at high speed.
Typifying many of these prior art seals are those found in U.S. Pat. Nos. 4,371,176; 4,427,203; 1,011,671; 3,979,128; 4,501,431; 3,871,666; 4,726,696; 3,194,571; 4,545,764; 3,831,950; 3,445,121; 4,257,617; and 4,501,431. Also, many of these seals are found in European Patent No. 724,301, German Patent No. 3,420,523, German Patent No. 884,262, and Japanese Patent No. 180,168.
Presently, mechanical seals or wear rings are commonly used for sealing against liquids when using a rotating shaft. These seals consist of radial planar surfaces which are normal to the shaft axis, see for example, the wear rings illustrated in FIG. 3, and Handbook on Pumps, October 1954, p. 83. The surfaces cooperate to function as a bearing. These wear rings often are constructed of metal, and therefore inherently possess the danger of "galling" or adhering upon contact, which can occur during start-up or when vibration occurs. This condition can cause a rapid failure of the seal.
During operation, the above seals can easily become worn or deteriorated, and the wear and deterioration can be non-uniform circumferentially about the shaft because of a number of reasons, such as misalignment of the shaft with respect to the machinery with which it is used, the seal becoming out of round or scarring due to rust or scale, or from harsh environments.
A labyrinth seal is another type of mechanical seal which is not fluid-tight but limits leakage by means of a tortuous path. The seal consists of a ring or a series of rings adapted to fit about a shaft with a goal to minimize leakage. A labyrinth seal offering advantages in terms of minimal leakage, is disclosed in commonly assigned, copending application, U.S. Ser. No. 150,222, entitled, Seal for a Rotatable Shaft, filed Mar. 25, 1988. This application discloses a dry seal which includes a single, elongated axially monolithic elastomeric sealing element, or a plurality of such sealing elements, each having a shaft side and a casing side. The shaft side is provided with a plurality of radially inwardly extending circumferential fins, each fin tapering towards an apex. The cross-section of each fin in a plane that includes the axis of the shaft is asymmetric. Two spaced fins define therebetween a circumferential purge chamber having at least one inlet which extends through the elastomeric sealing element to the purge chamber. The apices of the fins on each side of the purge chamber point in an axial direction away from the purge chamber. Each fin apex extends to the shaft, with minimal or substantially no clearance, when the seal is positioned about the shaft. Optionally, a plurality of adjacent fins having apices pointing in the same axial direction away from the purge chamber are provided on each side of the purge chamber to define therebetween a sealing chamber or chambers.
Despite the significant advances offered by that seal element, there remains a need for improved seals and assemblies comprising the same, particularly with respect to minimal leakage, long life expectancy and easy fabrication.
It is therefore an object of this invention to provide a self-aligning seal with improved performance and life expectancy, which minimizes friction between a seal and a rotating surface.
It is also an object of this invention to provide a seal which is efficient not only in terms of capabilities, but also in terms of its drastic reduction in down time of expensive machinery used in complex processes.
I have now found that the objects of this invention can be achieved by providing an improved labyrinth seal, which includes: compressible teeth having sufficient lubricity and memory which provide multiple seals on an axial axis and a radial axis for enhanced seal efficiency; a floating feature which allows the seal to float in place within prescribed tolerances and clearances, and which can withstand unstable conditions such as vibration or contact, and superior chemical resistance and mechanical properties.
The present invention thus provides a high efficiency labyrinth seal which minimizes leakage of fluid gas and/or solids along a shaft.